Decoding apparatus for television receivers



5 Sheets-Sheet 1 March 24, 1953 A. coTswoRTl-l `III, ETAL DECODING APPARATUS FOR .TELEVISION RCEIVERS Filed March 3. 1949 March 24, 1953 Filed March 5. 1949 Fig. 2

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DECODNG APPARATUS FOR TELEVISION RECEIVERS 5 Sheets-Sheet 2 TION OF DEC ODING APPARATUS CONTROL SIGNAL TO SECOND POR- ALBERT COTSWORTHIII RICHARD O. GRAY PIERCE E. REEVES IN1/Emol;

HIS AGENT DECODING APPARATUS FOR TELEVISION RECEIVERS 5 Sheets-Sheet 3 Filed March 5. 1949 l||||| wEE.

ALBERT COTSWORTHI RICHARD O. GRAY PIERCE EREEVES IN VEN TOR.

HIS AGENT March 24, 1953 A COTSWORTH m, ETAL 2,632,799

DECODING APPARATUS FOR TELEVISION RECEIVERS Filed March 3. 1949 5 Sheets-Sheet'fl Hor. Sync. To Def. Gener.

5| Blankihg Signal To CR. Tube ALBERT COTSWORTHIEI mno D RICHARD O GRAY PIERCE E. REEVES j JNVENroR. N

o L E g 2 BYM/of-M o 9 -S2 O D Q H|s AGENT March 24, 1953 DECODING APPARATUS FOR TELEVISION RECEIVERS Filed March 3. 1949 Fig-5 Bong U U U U U U A. coTswoR-rH nl ET AL 5 Sheets-Sheet 5 T|me ALBERT CoTswoRTH m RICHARD QGRAY PIERCE E. REEVES INVENToR.

His AGENT Patented Mar. 24, 1953 UNITED STATE OFFICE DECODING APPARATUS FOR TELEVISION RECEIVERS Application March 3, 1949, Serial No. 79,432

This invention relates to decoding apparatus for enabling a television receiver to decode and reproduce coded subscription television signals. It is particularly directed to decoding apparatus 'for enabling such receivers to decode and reproduce subscription television signals wherein the coding is manifested by variations during spaced operating intervals of the time relation of components constituting the television signal.

Copending application Serial No. 773,848, filed September 13, 1947, by Erwin M. Roschke, entitled Image `Transmission System, now U. S. Patent No. 2,547,598, issued April 3, 1951, and assigned to the present assignee, disclose a type of subscription television system to which this invention is especially applicable. In the Roschke system, television signals coded in a certain manner are radiated to subscriber receivers, and key signals for decoding the television signals are transmitted to the receivers over a line circuit, such as the telephone line. A metering device is included in the line circuit to each subscriber receiver to record the time of use of the key signal by the respective subscribers so that a suitable charge may be made to each subscriber for the subscription service. The coding in this system is effected by altering, at spaced time intervals, the timing of the video-signal component relative to the synchronizing-signal component of the television signal. The times of this alteration are indicated to the receiver by the key signal, and upon receipt thereof, decoding apparatus is actuated at a subscriber receiver to produce a compensating alteration in u a timing characteristic of the receiver so that it may decode and reproduce the television signal.

It is an object of the present invention to provide improved decoding apparatus for enabling a television receiver to decode and reproduce subscription television signals of the type in which the coding is effected by a change at spaced operating intervals of the timing of components constituting the television signal.

A more specific object of the present invention is to provide improved decoding apparatus for enabling a television receiver which is normally utilized .to reproduce television signals transmitted by present day conventional nonsubscription transmitters to be used in subscription systems such as the system disclosed in the aforementioned .Roschke application, to decode and reproducea coded .television `signa-lin which the coding is effected by a change at spaced oper- Claims. (Cl. 178--5.1)

2 ating intervals of the timing of components constituting the television signal.

The features of this invention whichare believed to be new are set `forth with particularity in the appended claims. The invention itself, however, together with further objects I'andadvantages thereof, may best be understoodbyreference to the following .description Whentaken in conjunction with the accompanying drawings, in which:

Figure 1 rshows a block ldiagram of a `television receiver incorporating the `present invention,

Figure 2 shows a circuit diagram of a'portion of the decoding apparatus or adaptor included in the receiver of Figure 1,

Figure 3 shows various curves useful V'in the understanding of the circuit of Figure 2,

Figure 4 shows a circuit diagram of a further portion of the decoding apparatus or adaptor included in the receiver of Figure 1, and

Figure 5 shows various curves useful in the understanding of the circuit of Figure 4.

Referring now to Figure 1, the televisionreceiver illustrated therein includes the usual cascade connected radio-frequency amplifier fI Oyrst detector II, intermediate-frequency amplifier I2, video detector I'3 and video amplifier '1"4. The input terminals of the radio-frequency ampliiier It may be connected to a suitable antenna I 5, and the output terminals of the `video amplifier I4 are connected to the control electrode and cathode of a receiver image reproducing device, or image tube, I6. A heterodyne oscillator `I'I is connected to the iirst detector I I. Output iterminals of the video detector I3 are also connected to the usual Asynchronizing-signal amplier and separator I8, the output vterminals lof which are connected to a vertical deflection Ygenerator I9 and to the synchronized oscillator portion 2G of the horizontal scanning systemof the receiver. The vertical deiiection generator I9 is connected to the vertical deflection coils ZI of the image tube I6. The unit 20 is coupled through decoding apparatus '22 to a horizontal deflection generator 23, this generator being connected to the horizontal deflection coils v2li of the image tube I6.

The decoding apparatus 22 provided in accordance with this invention may be constructed as an adapter for connection into the television receiver, or may be included as an integral part of the receiver. This decoding apparatus is connected to thesynchronized oscillator 20 `byfvvay of leads 25, and also to the horizontal Adeflection generator 23'by Way of leads `26, to thevertical 3 deflection generator I9 by Way of leads 21, to the cathode of the tube I8 by way of leads 28, and, finally, to a line circuit 29, which may be a telephone line extending to the receiver from the subscription transmitter, or other source of decoding signal.

This receiver, with the exception of the decoding apparatus Z2, is quite conventional and constructed in accordance with present day standards. Television signals received on antenna I5 are amplified in the radio-frequency amplifier I0, and heterodyned to an intermediate-frequency signal in the first detector Il. The intermediate-frequency signal from the first detector is amplified in the intermediate-frequency amplifier I2, and the video signal is detected by means of the video detector I3. The video intelligence from the detector I3 is amplified in the video amplifier I4, and `then impressed between the control electrode and cathode of the reproducing device I6 to control the intensity of the cathode ray beam in this device.

synchronizing-signal components of a received 'television signal are separated from the videofrequency components and amplified in the stage I8, and these synchronizing-signal components are used to synchronize the vertical deflection generator I9 and the horizontal deflection generator 23, to cause the image tube I8 to reproduce the image represented by the television signal. The apparatus required at the receiver to reproduce the accompanying sound-signal component of the received television signal forms no part of the present invention, and is not shown.

The function of the decoding apparatus 22 is to enable the receiver to reproduce a coded subscription television signal when the receiver is tuned to receive a signal of this type. The subscription television signal referred to is one which is transmitted in two modes, and accompanied by a key signal which the receiver obtains by means of the line 29. In the first mode of transmission of the subscription signal, the Videosignal and synchronizing-signal components thereof have a certain time relation with respect to each other. In the second mode these components have an altered time relation. The changes in mode in the subscription signal are effected at spaced operating intervals, and the key signal indicates to the receiver the times of these changes.

The decoding apparatus is coupled into the horizontal scanning system of the receiver between the synchronized oscillator stage 29 and the horizontal deflection generator 23. The decoding apparatus 22 is responsive to the coincidence of a burst of key signal received over the line circuit 29 and to a vertical-synchronizing pulse received over the leads 21, to change the timing of the horizontal-synchronizing pulses, passing from the leads 25 to the leads 28, at spaced time intervals determined by the bursts of key signal. The operation of the decoding apparatus in changing the timing of the horizontal-synchronizing pulses occurs in synchronism with similar changes in the time relation between the video-signal component of the received subscription signal and the synchronizing-signal components thereof. The decoding apparatus is arranged to alter the timing of the horizontal scanning of the image tube I8 in this manner by a correct amount and in the correct sense to compensate for such changes in the subscription television signal. Therefore, the tube I6 reproduces an undistorted image from this signal.

The decoding apparatus 22 also produces a blanking signal on the leads 28, vthe timing of which changes in correspondence with the alteration in the timing of the horizontal scanning of tube I6. This blanking signal is applied to the tube I6 and effectively blanks this tube during certain portions of the horizontal trace intervals in which the tube is not blanked by the horizontal blanking pedestals contained in the received signal. This blanking of the tube I6 by the blanking signal from the decoding apparatus 22 eliminates edge flicker which arises in the corrected reproduced image. A complete discussion of the cause and elimination of this edge flicker may be found in copending application Serial No. 14,821, filed February 5, 1949, entitled Subscription Type Signal Translating Apparatus, by Richard O. Gray, now U. S. Patent No. 2,572,853, issued October 30, 1951, and assigned to the present assignee.'

The decoding apparatus 22 may be considered as composed of two portions. The function of the first portion is to produce a control signal which changes characteristics in response to the next succeedingv vertical synchronizing pulse after the initiation of a burst of key signal, and also to the next suceeding vertical synchronizing pulse after the termination of such burst. This first portion is connected to the line circuit 29, and by means of leads 21, to the vertical deflection generator I9. The function of the second portion of the decoding apparatus is to alter the timing of the synchronizing signal from the synchronized oscillator 20 during intervals determined by the control signal, and to supply this synchronizing signal in its altered and unaltered state to the horizontal deflection generator 23, The external connections of the second portion, therefore, extend to the synchronized oscillator 20 and to the horizontal deection generator 23.

In this manner, the first portion of the decoding apparatus 22 actuates the second portion during the spaced operating intervals when the timing of the components of the received subscription signal is altered. The second portion of the decoding apparatus, in response to such actuation, controls the scanning of the image tube I6 to alter the timing thereof in a sense and by the correct amount to compensate for such alteration in the timing of the components.

The portion of the decoding apparatus 22 which is connected to the line circuit 29, and to the vertical deflection generator I9 as shown in Figure 2, and this portion comprises a pair of input terminals 40 which are connected to the primary winding 4I of a coupling transformer 42. One terminal of the secondary winding 43 o1 the transformer 42 is coupled to the control electrode 44 of the electron-discharge device 45 through a coupling capacitor 46, this control electrode being connected to ground through a grid-leak resistor 41. The other terminal of the secondary winding 43 is connected to ground .through a resistor 48. The cathode 49 of the discharge device 45 is connected to ground through a biasing resistor 59, this resistor being shunted by a by-pass capacitor 5I, and this cathode being further connected to the positive terminal of a source of unidirectional potential 52 through a resistor 53. The anode 54 of the device 45 is connected to the positive terminal of the source 52 through a load resistor 55, and this anode is coupled to one side of a rectifying device 56 through a capacitor 51. Regeneration is provided for the circuit of device 45 by means of a transformer 58. One terminal of the primary `winding 59 of the transformer 58 is directly connected to the common junction of the 'capacitor `51 and rectifying device 56, and the other terminal of this winding is connected directly to ground and is coupled to this common junction through a capacitor :60. One terminal of the secondary vWinding 6l of the transformer 5B is connected to ground, `and fthe other terminal of this winding is connected to the common junction of the resistor 48 and the Winding 43. The cathode 49 of discharge device '45 is connected to the cathode '62 of an v.electron-'discharge .device 63, and the other -side of the rectifyin-g device 56 is connected te the control electrode V64 .of device 63 through a resistor 55. The rectifying device 56 is also connected to `ground by means .of a resistor 35,5 connected 'to ythe common junction of device 56 `'and resistor B5, the resistor 66 being shunted by a capacitor .61. The anode 6B of device 63 is connected to the positive terminal of the source 52 through a load resistor 69.

One of a pair of vertical synchronizing pulse input terminals 1! is connected to ground. The other terminal 10 is coupled to the control electrode 54 through a series-connected resistor 1l and capacitor 12, and this terminal is also connected to the anode 68 through a series-connected resistor 13 and capacitor 14. the resistor 15 being connected between the anode 68 "and ground.

The anode 68 of the device 63 is coupled to the control electrode 16 of an electron-discharge device 11 through a capacitor 18, this control electrode being connected to ground through a gridleak resistor 19. The cathode 8S of device 11 is connected to ground through a biasing resistor 8 I, and the anode 82 of this device is connected to the positive terminal of source 52 through a load resistor 83. The cathode B of device 11 is directly connected to the cathode 84 of a discharge device 85, and the anode 82 of device 11 is coupled to the control electrode 86 kof device 85 through a coupling capacitor 31, the control electrode 86 being connected to the cathode 84 through a resistor 88. The anode 89 of device 85 is connected to the positive terminal of the source 52 through a load resistor Si?, and this anode is connected to ground through seriesccnnected resistors 9i, 92 and 93. The viunction of the anode 89 of device 85 and the resistor 5I is connected to the control electrode 1E of device 11 through a balancing resistor 94. One of the output terminals 8.5 is .connected to ground, and the other is connected to a movable tap 95 on the resistor 92.

The operation of the circuit of Figure 2 may best be understood by reference to Figure 3. Bursts o'f 'key'signaL Isuch as are indicated bv the curve 3A, are received over the line circuit 29 and impressed across the terminals 40. As previously stated, these bursts indicate the time intervals during which the timing of the video-signal component of the received subscription television signal is altered with respect to the synchronizing-signal component thereof. As pointed out in the Roschke application, the changes from the normal mode to the altered mode of transmission of the subscription signal are effected at the transmitter, preferably, during vertical retrace intervals to avoid distorting the television image, which would occur if such changes were made during trace intervals. As also pointed 'out in theRoschke application, each burst of key signal is preferably transmitted over the line c ircuit one .field period before the .corresponding :change in `inode `to .fallow for .delays 'that :usually :occur in this circuit. Therefore, the decoding apparatus at the receiver .must be arranged v'to receive these bursts 4in such amanner as .to enable the vertical-synchronizing pulse `succeeding the initiation of .each of Aith-ese bursts to actuate the decoding apparatus from a, first to :a Asecond position, and the vertical-synchronizing pulse succeeding the termination of each of these bursts to actuate the decoding apparatus from the sec- =ond .position back to itheirst position. With vthis arrangement, compensating changes at the receiver are made to koccur :simultaneously Vwith changes from mode to mode of the:receved subscription signal.

The bursts of .key signal .shown in the zcurve 3A, which vare.impressedacross :the terminals 1 40,

are amplied bythe circuit .of .the discharge 4de.- vice 45. The amplifier is made regenerative by reason of the connections of the transformeriS and resistor 48 which act to :supply a portion of the output signal of the device d5 back to the control electrode Alil .in proper phase to Vprovide such regeneration. To prevent noise signals and the like from affecting the decoding apparatus, the amplifier is made to respond only to signals above a certain threshold by reason of the positive bias on the cathode 49 due to the potentiometer -arrangement of the resistors 53 and '59. The amplified key signal bursts from the device 45 are rectified in the rectifying device 56 and negative-polarity pulses represented in `the curve 3B appear across the resistor'ii.

The vertical-synchronizing pulses derived from the generator i9 of Figure 1 are shown in the curve 3C, and these pulses are 'impressed across the terminals 1B by Way of the leads 21. The burst H00 of key signal shown in the curve 3A is initiated at the transmitter by a vertical-synchronizing pulse corresponding to the pulse IBI in curve 3C. Due to the possibilities of a time delay occurring in the line circuit 29, the burst I Du, when received by the receiver, may have shifted along the Ytime axis in relation rto the `initiating pulse lill which is received by air, and this shift is shown in Figure 3. However, as previously stated, the key signal bursts are transmitted a field period before a change in the transmitted signal from one Ymode to the other is made. Hence, such change in mode is made at the transmitter by the vertical-synchronizing pulse corresponding tothe pulse H32. Therefore, the decoding apparatus at the receiver,V under these circumstances, is arranged so that changes in the characteristics of thereceiver to compensate for such changes in mode are initiated by the vertical synchronizing pulse |02. To this end, the rectified negative-polarity bursts 'of key signal shown in 3B are impressed on the control electrode 64 of device 63. and the positive polarity vertical synchronizing pulses from the terminals 10 are also impressed on this control-electrode. The device 54 is arranged to have an ampliiication factor of 2, and its characteristics are such that in the presence of each rectified burst of key signal of the curve 3B the device is nonconductive and the vertical synchronizing pulses are not translated therebv. However, in .the .intervals between the rectified bursts of key signal, the device 63 is conductive and the positive polarity vertical synchronizing pulses applied to the control electrode 5A are amplied by this de.- vice and supplied to the control electrode 1611i the device 11 as negative polarity pulses of twice their original aniplitu'de. However, thepositive polarity vertical pulses are continuously supplied to the device '|I'by means of the circuit including the resistor 'I3 and capacitor 14. Therefore, the net result is that pulses are supplied to the control electrode I6 of the device TI which change polarity after the initiation and after the ter-I mination of each rectied burst, such pulses being shown in the curve 3D.

The discharge devices 'il and 85 are connected to constitute a conventional single-shot multivibrator circuit. Assuming that in the initial state of the multivibrator circuit the device 85 is conductive and device 'I1 is non-conductive, the multivibrator is maintained in this initial state until a positive polarity pulse, such as the pulse |03 of the curve 3D trips the multivibrator into its secondary state. yPositive pulses immediately succeeding the pulse |03 have no effect on the multivibrator; but the next negative pulse, such as the pulse |04 of the curve 3D, acts to return the multivibrator to its inital state,

Therefore, a control signal such as shown in the curve 3E is obtained across the resistors 9|, 92 and 33 and hence across the terminals 95, the amplitude of this Vcontrol'signal appearing across the terminals 95 being adjustable by means of the variable tap SS. This control signal has amplitude changes determined by the vertical synchronizing pulses immediately succeeding the initiation and termination of the individual bursts of key signal received on the line 29. Therefore, the amplitude changes in the control signal from a minimum to a maximum and from a maximum to a minimum occur in synchronism with changes in mode of the received subscription television signal.

The control signal shown in the curve 3E is impressed across the terminals of the circuit of the second portion of the decoding apparatus shown in Figure 4. The pulses of this control signal actuate this second portion to change the timing of the horizontal synchronizing signals passing therethrough during spaced time intervals corresponding to the intervals during which the received subscription television signal is in its second or altered mode.

The circuit or" Figure 4 includes a pair of input terminals ||I which are connected to the synchronized oscillator 20 of Figure 1 by Way of the leads 25. The terminals are further coupled to the primary Winding 2 of a transformer I3 through a series-connected resistor I I4 and capacitor II5. One end of the secondary winding IIS of the transformer I I3 is grounded, and the other end is coupled to the control electrode I I'I of an electron-discharge device |I8 through a seriesconnected resistor I I9 and capacitor 20. The common junction of the winding I I6 and the resistor I I9 is coupled to ground through a capacitor I2I, and the common junction of resistor |I9 and capacitor |20 is coupled to ground through a capacitor |22, resistor ||9 and capacitor |22 forming a phase shifting network.

One of the terminals |I0, is grounded and the other is connected to the control electrode ||1 of the device IIS through a series-connected resistor |23 and an adjustable resistor |24. The device I I8 is connected as a conventional blocking oscillator. The anode |25 of this device is connected to the positive terminal of a source of unidirectional potential |28` through the Winding |27 lof a transformer |28. The cathode |29 of the device I I8 is coupled to ground through the winding |30 of the transformer |28 and a seriesconnected resistor |3I. 'Ihe anode |25 of device 4 ||8 is connected to one of the output terminals |32, the other of these terminals being grounded. The terminals |32 are connected to the horizontal deflection generator 23 of Figure 1 through leads 20.

The common junction of the resistor |3| and the winding |30 is coupled to the control electrode |33 of an electron-discharge device |34 through a series-connected capacitor |35 and a resistor |36, the control electrode |33 being connected to ground through a grid-leak resistor |31. The device |34 and a further electron-discharge device |33 are connected to form a conventional single-shot multivibrator circuit. The anode |39 of the device |34 is connected to the positive terminal of the source |26 through a load resistor |40, and this anode is coupled to the control electrode |4| of the device |38 through a coupling capacitor |42, this control electrode being connected to ground through a series-connected adjustable resistor |43 and a resistor |44. The cathode |45 of the device |34 is directly connected to the cathode |46 of the device |38, and these cathodes are connected to ground through a common cathode resistor |41. The anode |48 of the device |38 is connected to the positive terminal of the source |26 through a series-connected resistor |49 and a radio-frequency choke coil |50. The anode |48 is also connected to one of the output terminals I5I, the other of these terminals being grounded. The output terminals I5I are connected to the cathode of the image tube I5 of Figure 1 by Way of the leads 28.

The operation of the portion of the decoding apparatus shown in Figure 4 may best be understood by reference to Figure 5. The curve 5A shows the control signal which is impressed across the terminals H0. This control signal is the signal shown by the curve 3E of Figure 3, but is illustrated herein on an expanded time base for purposes of clarity. The control signal is impressed on the control electrode II'I of the discharge device IIB, and its amplitude and, hence, the timing of the blocking oscillator may be adjusted by adjustment of the tap of Figure 2. The output signal from the synchronized oscillator 28 of Figure 1 is applied to the terminals 25 and this signal has the usual form, as shown by the curve 5B, with negative sine Wave peaks occurring at the horizontal synchronizing frequency of the received signal. These peaks are passed through a network which consists of the resistor |I4, the capacitor I5 and the primary winding I i2 of the transformer I3, and they appear across the secondary winding IIE -asa sine wave having a frequency equal to the horizontal synchronizing frequency, the secondary Winding and capacitor 2| forming a resonant circuit tuned to the repetition frequency of the sinewave peaks. This sine Wave is phase shifted in the network H9, |22 and the phase shifted sine wave, together with the control signal of the curve 5A, are impresed upon the control electrode II1 of the blocking oscillator discharge device I|8. The combined signal impressed thereon has the form shown in the curve 5C.

The signal impressed on control electrode ||1 of the device I8 controls the timing of the blocking oscillator. The triggering point of the blocking oscillator discharge device I I8 is shown by the dotted line ||5 of the curve 5C, and may be adjusted by adjustment of resistor |24, since this resistor, together with the resistors 82 and 83 of Figure 2, forms the discharge path of the capacitor |20. Whenever the signal on the control elecacea'zea trede H1 increases-in a positive direction across the dotted line H5, the blockingl oscillator is actuated from one condition to the other. Hence, when the control signal of the curve 5A has a minimum amplitude, the sine Wave. portion of the curve 5C triggersthe blocking oscillator at the points designated as m,.and.when this control signal has a maximum amplitude, the sine Wave trips the blocking' oscillator at the. points designated asy. Therefore, during the intervals When the maximumA amplitude portion of the control signal of 5A isv present, the timing of the blocking oscillator is advanced a. certain. time interval designated as t. As previously stated the value of the time interval t can be varied by adjustment of the tap 96, which adjustment controls the amplitude of the. maximum potential portion of the control signal applied to the control electrode H1 of the device I I8.

Each time the blocking oscillator is triggered, a signal. such as shown in the curve 5D appears at the anode |25 of the device H8. This signal has negative-polarity peaked portions E55 and positive-polarity pulse portions l56, as shown. The positive-polarity pulses l5@ of the curve 5D appear across the terminals 132 and are used to synchronize the horizontal deflection generator 23 of Figure 1 With the horizontal synchronizingsignal component of the received television signal.

The timing of the, pulses 56 of the curve 5D is changed each time the mode of transmission of the television signal is changed, and therefore the timing of the horizontal scanning of the image tube I6 of Figure 1 is altered in synchronism with such changes in mode. The arrangement is such that such alteration of the timing of the horizontal scanning of the image tube is of the correct amount and in the appropriate sense to compensate for changes in mode in the received subscription signal and to enable the image tube to reproduce an undstorted image from this signal.

To blank the image tube l5 at appropriate intervals and thus avoid edge flicker in the reproduced image, the decoding apparatus is arranged to produce blanking pulses which are impressed on the cathode of this tube. The timing of the blanking pulses is altered concurrently with the timing of the horizontal synchronizing pulses from the decoding apparatus 22 as the received subscription television signal changes from one mode to the other. To produce such blanking pulses, the peaked pulses of positive polarity shown in the curve 5E and which appear across the cathode resistor IBI, are used to trigger a multivibrator which is formed by the circuit of the devices |34 and 33. The multivibrator circuit has a time constant shorter than the intervals between the pulses -of the -curve 5E. This time constant may be adjusted by means of the variable resistor |43, and therefore pulses shown in the curve 5F appear across the output terminals IBI, these pulses each having a leading edge determined by the pulses of the curve 5E and an adjustable trailing edge. The pulses of the curve 5F' are applied to the cathode of the image tube It of Figure 1, and by adjustment of the resistor U33 can be caused to blank this tube duringv portions of the scanning intervals that the tube Would otherwise be unblanked. It is noted that the timing of the pulses in the curve 5F changes each time there is a change in mode in -the received subscription television signal. Therefore, by proper adjustment of the resistor |43, the pulses of 5F blank the image tube for certain intervals during one mode of the received 10 signal andfor other intervals during the other mode of this signal, thereby eliminating edge flicker inthe reproduced image, as fully explained in the aforementioned Gray application.

This invention provides, therefore, improved decoding apparatus for enabling a television re.- ceiver to decode and reproduce a subscription type television signal in which the timing between components constituting the signal is altered during spaced operating intervals to effect coding thereof.

The decoding apparatus disclosed herein may be constructed integrally into a receiver, and furthermore finds great utility in that it may be constructed as a separate unit and connected into existing televisionl receivers that are not equipped to reproduce subscription television signals, to

adapt such receiversy toY decode and reproduce such signals of the aforedescribed type.

While a certain specic embodiment of the invention has beenshown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as fall Within the true spirit and scope of this invention.

We claim:

l. Decoding apparatus for enabling a television receiver to reproduce images in response to a coded television signal including video and synchronizing componentsA having a -time relation that is altered in accordance with a coding schedule, and to a key signal received concurrently With said television signal and having characteristie variations representing said coding schedule, said apparatus comprising: a trigger circuit responsive to an appliedcontrol signal for producing recurring output pulses individually initiated when the amplitude of said control signal exceeds a given value; a first control circuit coupled to said trigger circuit and responsive to said synchronizing components for supplying thereto a periodic control signal having in each cycle a.

sloping portion which exceeds said given amplitude value in xed time relation with respect to each of said synchronizing components; a second control circuit for developing control pulses; a network for utilizing the aforesaid key signal to supply an actuating signal to said second control circuit to actuate said second control circuit in accordance with said coding schedule; and means for applying said control pulses to said trigger circuit effectively as a pedestal for said periodic control signal thereby to vary in accordance with saidschedule the timeA when the amplitude of said sloping portion of eachv cycle of said periodic control signal exceeds said given amplitude value.

2. Decoding apparatus for enabling a television receiver to reproduce images in response to a coded television signalv including video and synchronizing components, having a time relation that is. altered, by a preselected amount during spaced time, intervalaand to a key signal received concurrently with, said television signal and having characteristic variations indi'cating said spaced intervals,- said apparatus comprising: a trigger circuit, responsive to an applied control signal for producing recurring. output-pulses individually initiated when the-amplitude of said control signal; exceeds a given4 value; a rst control circuit coupled to-said-trigger circuit andl including a tuned network resonant. at the repetition frequency of said synchronizing components and responsive to said synchronizing components for supplying to said trigger circuit a sine-wave control signal having in each cycle a sloping portion aesa'ca which exceeds said given amplitude value in fixed time relation with respect to each of said synchronizing components; a second control circuit lfor developing control pulses; a network for utilizing the aforesaid key signal to supply an actuating signal to said second control circuit to actuate said second control circuit during said spaced intervals; and means for applying said control pulses to said trigger circuit effectively as a pedestal for said sine-Wave control signal thereby to vary by said preselected amount the time when the lamplitude of said sloping portion of each cycle of said control signal exceeds said given amplitude value.

3. Decoding apparatus for enabling a television receiver to reproduce images in response to a coded television signal including video components and verticaland horizontal-synchronizing componen-ts, said video and horizontal-synchronizing components having a time relation that is altered by a preselected amount during spaced intervals and to a key signal received concurrently with said television signal and having characteristic variations indicating said spaced intervals, said apparatus comprising: a trigger circuit responsive to an applied control signal for producing recurrent output pulses individually initiated when the amplitude of said control signal exceeds a given value; a rst control circuit coupled to said trigger circuit and responsive to said horizontal-synchronizing components for supplying thereto a periodic control signal having in each cycle a sloping portion which exceeds said given amplitude value in xed time relation to each of said horizontal-synchronizing components; a second control circuit actuable from a iirst to a second operating condition for supplying control pulses to said trigger circuit effectively to vary by said preselected amount the time when the amplitude of said sloping portion of each cycle of said control signal exceeds said given amplitude value; and a network responsive jointly to said verticalsynchronizing pulses and said key signal for supplying actuating pulses to said second control circuit during said spaced intervals.

' 4. Decoding apparatus for enabling a television receiver to reproduce images in response to a coded television signal including video components and verticaland horizontal-synchronizing c omponents, said video and horizontal-synchronizing components having a time relation that altered by a preselected amount during spaced intervals and to a key signal received concurrently with said television signal and having characteristic variations indicating said spaced intervals, said apparatus comprising: a trigger circuit responsive yto an applied control signal for producing recurrent output pulses individually initiated when the amplitude of said control signal exceeds a given value; a first control circuit coupled to said trigger circuit and responsive to said horizontal-synchronizing components for supplying thereto a periodic control signal having in each cycle -a sloping portion which exceeds said given amplitude value in xed time relation to each of said horizontal-synchronizing components; a second control circuit, actuable from a first to a second operating condition in response to actuating pulses of one polarity and actuable from said second to said first operating condition in response to actuating pulses of a second polarity, for supplying control pulses to said trigger circuit eectively to vary by said preselected amount the time when the amplitude of said sloping portion of each cycle of said control signal exceeds said given amplitude value; and a network responsive to said vertical-synchronizing components for supplying actuating pulses of said one polarity to said second control circuit, and responsive tol the joint application of said vertical-synchronizing components and said key signal for supplying actuating pulses of said second polarity to said second control circuit, to cause said second control circuit to produce said control pulses during said spaced intervals.

5. Decoding apparatus for enabling a televisionl receiver to reproduce images in response to a coded television signal including video components and Verticaland horizontal-synchronizing components, said video and horizontal-synchronizing components having a time relation that is altered by a preselected amount during spaced intervals, and to key-signal bursts received over a line circuit and indicating said spaced intervals, said apparatus comprising: a trigger circuit responsive to an applied control signal for producing recurrent output pulses individually initiated when the amplitude of said control signal exceeds a given value; a first control circuit coupled to said trigger circuit and including a tuned network resonant at the repetition frequency of said horizontal-synchronizing components and responsive to said horizontal synchronizing components for supplying to said trigger circuit a sine-Wave control signal having in each cycle a sloping portion which exceeds said given amplitude value in xed time relation to each of said horizontal-synchronizing components; a second control circuit, actuable from a first to a second operating condition for supplying control pulses to said trigger circuit eiiectively to vary by said preselected amount the time when the amplitude of said sloping portion of each cycle of said control signal exceeds said given amplitude value; a rectifying circuit connected to said line circuit for rectifying said key signal bursts; and a network coupled to said rectifying circuit responsive to said vertical-synchronizing components for supplying actuating pulses of one polarity to said second control circuit; and responsive to the joint application of said vertical-synchronizing components and said rectified key-signal bursts for supplying actuating pulses of a second polarity to said second control circuit, [to cause said second control circuit to produce said control pulses dur' ing said spaced intervals.

ALBERT COTSWORTI-I III. RICHARD O. GRAY.

.REFERENCES CITED The following referencesare of record in th file of this patent:

UNITED STATES PATENTS 

